mRNA flu vaccine sustains germinal centers to broaden antibody responses, study finds

Influenza has long been one of medicine’s most stubborn adversaries, not because the virus cannot be countered, but because it refuses to stand still. Through continual antigenic drift, the hemagglutinin and neuraminidase proteins on the viral surface accumulate mutations that erode the protective power of antibodies generated by previous infections and vaccinations. This molecular shapeshifting is the reason seasonal influenza vaccines must be reformulated and re-administered almost every year, and why vaccine-induced protection often wanes well before a flu season ends. For researchers, the central challenge is clear: design vaccines that do more than mount a narrow, short-lived response against a handful of circulating strains, and instead coax the immune system into producing broader, more durable antibody repertoires capable of recognizing an evolving virus.

A new study from Korea University College of Medicine, published in Nature Immunology on June 15, 2026, offers a detailed molecular portrait of how an mRNA-based influenza vaccine may accomplish exactly that. Led by Associate Professor Jiwon Lee of the Department of Convergence Medicine and the Vaccine Innovation Center, and conducted in collaboration with Professor Ali Ellebedy and his group at Washington University in St. Louis, the investigation compared an investigational quadrivalent mRNA influenza vaccine, designated mRNA-1010, against the licensed conventional split-virion vaccine Fluarix in a head-to-head clinical evaluation. The central question was whether the mRNA platform could stimulate stronger and more persistent germinal-center responses than a conventional vaccine, and whether that persistence would translate into a measurably broader antibody repertoire in the blood.

The germinal center is the crucible where vaccine-induced immunity is forged. Within specialized microenvironments of draining lymph nodes, B cells that recognize vaccine antigen undergo rounds of proliferation, somatic hypermutation, and selection. Each cycle introduces random mutations into the genes encoding the B-cell receptor, and only those variants whose mutated receptors bind antigen with higher affinity are permitted to survive and expand. Over weeks, this Darwinian process generates plasma cells that secrete high-affinity antibodies and memory B cells that persist for years. The duration and intensity of germinal-center activity are therefore widely regarded as key determinants of both the breadth and the durability of antibody responses. A vaccine that keeps germinal centers active for longer gives B cells more opportunities to mutate, diversify, and explore antibody solutions that recognize conserved or varied features of the virus.

To test whether mRNA vaccination extends this critical phase, the researchers enrolled 75 healthy adults aged 20 to 50 years and followed them across two influenza seasons. Of these, 38 participants received mRNA-1010 and 37 received Fluarix. Blood samples were collected at multiple time points through 26 weeks after vaccination, allowing the team to track the evolution of circulating antibodies over nearly half a year. Crucially, a subset of participants also underwent ultrasound-guided fine-needle aspiration of draining axillary lymph nodes, an invasive but informative procedure that enabled direct sampling of germinal centers as they formed and matured. This combination of peripheral blood monitoring and lymph-node sampling is rare in human vaccine studies and gave the investigators an unusually complete view of the immune response as it unfolded in real time.

The laboratory analysis was correspondingly comprehensive. The team deployed flow cytometry to characterize immune cell populations, ELISpot assays to quantify antigen-specific antibody-secreting cells, single-cell RNA sequencing and B-cell receptor sequencing to resolve individual B-cell lineages, serum IgG proteomics to catalog circulating antibody clonotypes, and a battery of antibody binding and neutralization assays to test functional activity against antigenically diverse influenza strains. Together, these methods profiled the response at scales ranging from single cells to whole serum, providing a multidimensional dataset that conventional vaccine trials, which typically rely on bulk antibody titers alone, cannot match.

The findings were striking. The mRNA vaccine elicited a substantially more diverse and broader serum antibody repertoire than Fluarix, according to Dr. Lee. Most notably, influenza-specific germinal-center responses persisted for up to 26 weeks in 5 of 13 mRNA-1010 recipients whose draining lymph nodes were sampled, while persistent germinal centers were not detected among any of the Fluarix recipients sampled. Six months of sustained germinal-center activity after a single vaccination is an unusually long window of B-cell evolution, and it suggests that the mRNA platform provides antigen persistence and inflammatory signaling that keep the selection machinery running far longer than a conventional protein-based split-virion preparation.

That prolonged activity left a measurable imprint on the antibody repertoire. The mRNA vaccine increased the diversity of the serum IgG repertoire and promoted the diversification of pre-existing B-cell lineages through somatic hypermutation, meaning that antibodies the immune system had already learned to make against earlier influenza exposures were not merely recalled but actively refined and expanded. These molecular changes were associated with broader antibody binding across antigenically diverse influenza strains and with significantly greater increases in neutralization titers against 11 of 13 A/H1N1 viruses tested. In practical terms, the antibodies generated after mRNA vaccination recognized a wider range of viral variants and neutralized more of them, including strains that differed antigenically from those contained in the vaccine itself. Dr. Lee summarized the distinction succinctly: the mRNA platform does not simply produce more antibodies, it produces a more diversified antibody response, which leads to greater binding and neutralizing breadth.

A key methodological strength of the study was Ig-Seq, a mass-spectrometry-based technology that identifies individual antibody clonotypes circulating in the blood after vaccination. Conventional vaccine studies typically measure bulk binding or neutralization titers, aggregate numbers that reveal how much antibody activity is present but say little about its composition. Ig-Seq resolves the response down to individual antibody clonotypes, revealing which antibody lineages emerged, expanded, and diversified after vaccination. Combined with B-cell receptor sequencing, this molecular-level approach allowed the researchers to trace the genealogical trees of antibody families as they mutated and branched over the six-month observation period, directly linking sustained germinal-center activity in the lymph node to the diversification of antibodies measurable in the serum. The authors identify Ig-Seq as a defining strength of the work because it captures information that bulk serology fundamentally cannot.

The broader implications reach toward the long-sought goal of a more universal influenza vaccine. If mRNA vaccination can sustain germinal-center activity for months rather than weeks, it creates a temporal window in which B cells can accumulate mutations that broaden their recognition of the virus’s antigenic landscape. This mechanism could in principle support protection that carries over between seasons, reducing the need for annual reformulation and re-vaccination. However, the authors are careful to note that further studies are needed to determine whether these broadened responses translate into multi-season protection or permit longer vaccination intervals. The study population consisted of healthy adults aged 20 to 50, and future research must investigate whether the same benefits are maintained in older adults and immunocompromised populations, whose germinal-center function, B-cell repertoire diversity, and overall immune responsiveness differ substantially from those of healthy younger recipients.

What the study establishes, with unusual molecular resolution, is a mechanistic bridge between a vaccine platform and the quality of the immunity it generates. Persistent germinal centers, diversified B-cell lineages, and a broader serum antibody repertoire form a coherent causal chain, and tools such as Ig-Seq now make each link observable in humans. As mRNA technology matures beyond its first applications, findings like these suggest that its most consequential contribution to vaccinology may lie not in speed of development but in the depth and breadth of the immune memory it leaves behind, offering a rational template for influenza vaccines designed to stay ahead of a virus that never stops changing.

Subject of Research: A clinical study comparing mRNA-1010 and Fluarix influenza vaccines in healthy adults, examining germinal-center persistence and antibody repertoire breadth

Article Title: Korea University study uncovers how mRNA vaccination may broaden flu antibody responses

Article References: Korea University study uncovers how mRNA vaccination may broaden flu antibody responses. (n.d.). Original publication

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Keywords: mRNA vaccine, influenza, germinal center, antibody breadth, B cells, somatic hypermutation, Ig-Seq, neutralization, vaccinology, Nature Immunology, Korea University, immune repertoire